1. Field of the Invention
The present disclosure relates to new block copolymers, directed self-assembly compositions, and methods of directed self-assembly pattern formation in the fabrication of microelectronic structures.
2. Description of the Prior Art
The real resolution limit for single patterning 193 nm immersion scanners is becoming insufficient to keep up with the pace of technology advancement. To keep Moore's law moving forward, non-lithography techniques will become more and more important. Directed self-assembly (DSA) techniques are already capable of forming patterns that are <15 nm. DSA is quickly becoming a front-running technology for forming patterns of <20 nm for integrated circuit (IC) manufacture.
Currently, the use of DSA for generating lines and spaces utilizing conventional polystyrene (PS) and poly(methylmethacrylate) block copolymer (PS-b-PMMA) has shown to be in the critical dimension range of 10-20 nm pitch. A range of methods using both chemoepitaxy and graphoepitaxy pre-patterning process flows have been successful for creating both lines and spaces (lamellae) and contacts (cylinders). In contrast, the resolution limit for single patterning 193 nm immersion scanners is 37 nm for dense lines and spaces and 40 nm for contact openings.
Typical DSA process flows incorporate several layers. DSA of block copolymers (BCPs) typically is performed on an organic, neutral “brush” layer. This brush layer usually consists of a random copolymer of styrene and methyl methacrylate (PS-r-PMMA) that has been cured over a long period of time. The block co-polymer DSA formulations are then coated on top of the brush layer and annealed. The annealing process causes the block co-polymer to arrange itself into alternating organized structures. Optionally, a bottom anti-reflective coating is used to control reflection control of a pre-pattern. This pre-pattern is often formed by standard photolithography techniques, such as the patterning of a photoresist. Etch block layers are also included under the DSA layers to facilitate the pattern transfer process (a silicon- or metal-containing hardmask (IM) such as SiO2 or TiN). Another etch transfer layer, such as spin-on carbon (SOC), may also be under the HM layer in the DSA stack.
Current DSA process flows utilize BCP DSA formulations that are coated to a thickness of around 200-400 Å and annealed. After successful annealing, one of the blocks can then be etched away with the remaining block used as an etch block for the underlying layers or substrate. In a typical PS-b-PMMA BCP formulation, the PMMA etches faster than PS in dry etch conditions. The PMMA is typically all removed while the PS remains on the substrate. During the PMMA removal step, however, significant thickness loss of PS also occurs. Measurements of remaining PS can be as low as half of the original thickness (i.e. 400 Å thickness of PS is reduced to 200 Å or less). FIG. 1 demonstrates this problem. A transfer layer 10 is on a substrate (not shown) or potentially on optional intermediate layers. After a prior art PS-b-PMMA coating is applied and annealed, the assembled PS regions 12 and PMMA regions 14 are formed to create patterned layer 11. Post-annealing, the thickness of patterned layer 11 is typically 20-40 nm. The PMMA regions 14 are then etched (typically dry etching, such as O2 or Ar plasma) to create lines 12 (i.e., the remaining PS region 12) and spaces or contacts 16. The original PS regions 12 experience etching during this process as well, albeit more slowly than the PMMA regions 14, thus leaving insufficient thickness of the lines 12 for the remaining etching that is needed to fully transfer through the transfer layer 10, as shown in FIG. 1(c).